1. Field of the Invention
This invention relates to a method for specifically detecting an analyte having specific bonding properties, such as a nucleic acid, an endocrine disruptor and an antigen, using photocurrent. This invention also relates to an electrode, a measuring cell and a measuring device which are used for this method.
2. Background Art
Genetic diagnoses for analyzing DNA in a biological sample are promising as new diagnoses and prevention techniques for various diseases. The following techniques are proposed for simply and accurately conducting such DNA analysis.
A method for analyzing DNA is known in which the analyte DNA is hybridized with a fluorescence-labeled DNA probe having a sequence complementary to that of the analyte DNA, and a fluorescent signal generated in the hybridization is detected (see Japanese Patent Laid-Open Publication No. H7-107999 and Japanese Patent Laid-Open Publication No. H11-315095, for example). The method uses dye fluorescence to detect the double-stranded DNA synthesized by hybridization.
Another method is also known in which, after a gene sample denatured to single-stranded DNA is hybridized with a single-stranded nucleic acid probe complementary to the gene sample, a double-stranded nucleic acid recognizing substance, such as an intercalator, is added thereto for electrochemical detection (see Japanese Patent Publication No. 2573443 and Surface Science Vol. 24, No. 11, pp. 671-676, 2003, for example).
On the other hand, damage to a genital system, a nervous system and the like due to an endocrine disruptor (environmental hormone), such as dioxin, has recently caused a social problem. At present, various methods are employed for detecting the toxicity of the endocrine disrupter, but such substance exhibits the toxicity at a significantly low level of concentration around 10 ppt. Accordingly, it is required to provide a method for detecting an endocrine disruptor within such a low concentration range.
In particular, the endocrine disruptor binds to the target DNA through a protein serving as a receptor or the like, thus affecting the expression of the DNA and the like to cause toxicity. Specifically, the endocrine disruptor does not bind directly to the DNA, but binds indirectly to the DNA through the protein serving as the receptor or the like. For this reason, in a conventional method, such as a prescreening technique using DNA bonding properties, it is not easy to assay the bond.
Incidentally, there is known a solar cell using a sensitizing dye for generating electric energy from light (see Japanese Patent Laid-Open Publication No. H1-220380, for example). The solar cell comprises a polycrystalline metal oxide semiconductor and a sensitizing dye layer deposited on a large area of the surface of the semiconductor.
As an approach to applying the characteristics of the solar cell to biochemical analysis, use of photocurrent generated by photoexciting the sensitizing dye for detecting an analyte (biomolecules such as DNA and protein) has been proposed (see Japanese Patent Laid-Open No. 2002-181777 and “New detection method of DNA double-stranded using photoelectric conversion” by Nakamura, et al. (prepared lecture texts of the Chemical Society of Japan, Vol. 81ST No. 2 (2002), page 947), for example).